Method and device for detecting a phase of a four-stroke gasoline engine

ABSTRACT

A method and a device for detecting the phase of a four-stroke gasoline engine, a gasoline direct injection engine in particular. For reliable phase detection involving relatively little expense during a starting phase, a crankshaft is turned together with at least one piston; ignition is triggered via an ignition coil in at least two successive top dead centers of the piston without a supply of fuel. A primary current or a secondary current, or a primary voltage or a secondary voltage are measured in a measuring period which extends at least over a spark duration after the ignition. From the comparison of the measuring signals of successive ignitions, a conclusion is drawn as to which of the successive top dead centers is an ignition top dead center and which is a charge cycle top dead center.

FIELD OF THE INVENTION

The present invention relates to a method and a device for detecting aphase of a four-stroke gasoline engine.

BACKGROUND INFORMATION

In engines whose fuel injectors are electronically controlled via an ECU(electronic control unit) it is necessary to determine the phaseposition at the start of the internal combustion engine. Since acombustion cycle extends over two 360° revolutions of the crankshaft, itis only determined via the phase position whether the piston is in thecompression stroke or in the exhaust stroke during the upward motion.

Different systems are known in this connection. An additional transducerwheel may be provided on the camshaft or coasting detection may beperformed. Such systems require additional expensive means.

Furthermore, in multipoint injection engines, the phase may bedetermined in what is known as a twin ignition system via fuel injectionand ignition at the successive top dead centers.

Each second ignition finds an ignitable fuel mixture. Depending on thephase position, the injection takes place in the form of storageupstream from the closed intake valve or during the intake stroke withthe intake valve open. However, unburnt air/fuel mixture is never pushedinto the catalytic converter in engines having multipoint injection.After the engine is started, one may subsequently switch to singleignition in the I-TDC (ignition top dead center) using other TDCdetection methods.

However, such a twin ignition system including ignition and injection ineach crankshaft revolution may not be used in a gasoline directinjection (GDI) engine since, in these engines, injection must takeplace precisely during the intake stroke or at the beginning of thecompression stroke, and injection during the exhaust stroke is notpermitted, since otherwise unburnt fuel may be pushed out into thecatalytic converter.

German Patent Application No. DE 198 17 447 describes a method and adevice in which, during a starting phase, the crankshaft is turned by astarter and, for each crankshaft revolution, a voltage is applied to thespark plug at the approximate time of the appropriate top dead centerwithout injection. Paschen's law, according to which the greater thepressure between the electrodes, the higher the ignition voltage, isused for detecting the phase. If the engine is turned by the starter,compression of the gas in the combustion chamber takes place only duringthe compression strokes, the highest pressure being reached at theignition top dead centers (I-TDC) which are offset by a 720° crankshaftangle. A noticeably lower gas pressure is present in the charge cycletop dead centers (CC-TDC) between the exhaust stroke and the intakestroke, offset with respect to the I-TDCs by 360°. To differentiate theI-TDC from the CC-TDC, an ignition voltage is set which is onlysufficient for ignition at the low pressure of the CC-TDC, but not atthe high pressure of the I-TDC. For setting the ignition voltage, onlyan adequate ignition power is supplied to the ignition coil. An ioncurrent analysis is performed to differentiate whether or not anignition took place in the particular top dead center. If no ignitionoccurred, only a short half-wave, interrupted by the freewheeling diode,is measured in the primary circuit and the secondary circuit due to thecomponent capacitances and the inductance of the particular ignitioncoil winding. However, an essentially triangular secondary current ismeasured as spark current in the event of an ignition.

The method and the device described in German Patent Application No. DE198 17 447 may also be used in a GDI engine since ignition at the CC-TDCtakes place without injection. A precise triggering of the ignition coilmust initially take place in order to make the desired ignition poweravailable. The required threshold value of the ignition power fordifferentiating the top dead centers may turn out to be different, inparticular in different engines, so that a precise adjustment isdifficult. Furthermore, analysis of the ion current measured for aprecise differentiation between I-TDC and CC-TDC is relatively complex.

SUMMARY

A method and device according to an example embodiment of the presentinvention may have an advantage over the related art due to the factsthat they may be achieved relatively inexpensively, they may makeprecise detection of the phase possible, and, in particular, they mayalso be used in a gasoline direct injection engine. Following phasedetection, the engine may advantageously be started via correctinjection and ignition according to the phase with the crankshaftalready rotating.

Thus, according to the present invention and in contrast to theabove-mentioned twin ignition systems, the engine is turned usingignition and without using injection. In contrast to German PatentApplication No. DE 198 17 447, adequately high ignition power issupplied, resulting in an ignition at each crankshaft rotation withouthaving to set a precise threshold value.

The example embodiment of the present invention is based upon therecognition that differentiation of the I-TDC from the CC-TDC is alsopossible when an ignition is executed in both top dead centers, sincethe ignition behavior is different in both positions. Due to the highpressure, the ignition voltage is high and the spark duration is shortat I-TDC; whereas at CC-TDC the ignition voltage is low and the sparkduration is long. The two positions may thus be differentiated after theoccurrence of the ignitions by comparing the spark durations, theignition current, or the ignition voltage applied to the spark plug.

According to one embodiment, the secondary current may be measuredvis-à-vis ground, as a voltage drop for example, across a shunt resistorwhich is connected in series to the secondary winding of the ignitioncoil and the spark plug. In this case, the measuring device is formed ina simple manner by the shunt resistor in the secondary circuit. Thevoltage drop across the shunt resistor is picked up by an analyzingdevice in the form of a measuring signal.

A measurement in the primary circuit may be carried out in particularvia the primary voltage which is tapped at the primary winding terminalsof the ignition coil. In this case, a suitable measuring circuit havingan operational amplifier or comparator may be used as a measuringdevice, and the primary voltage may be supplied, via a voltage dividercircuit for example, to an input of the operational amplifier forcomparison with a reference voltage at the other input of theoperational amplifier. The operational amplifier in turn supplies ameasuring signal to an analyzing device.

In both embodiments, the analyzing device may advantageously pick up thecontrol signal of the ignition transistor in addition to the respectivemeasuring signal in order to be able to determine the moment of ignitionfor the analysis of the measuring signal.

The analyzing device outputs a spark duration signal to a comparatorwhich compares the spark duration signals with each other or withpre-stored values, thereby assigning a shorter spark duration to theignition at I-TDC.

The phase detection method according to the present invention may becarried out on one piston or simultaneously on multiple pistons. Afterthe phase detection is executed, the crankshaft rotation may be used forthe starting operation by using correct injection and ignition accordingto the phase in the next I-TDC.

In contrast to phase detections via discharge detection or an additionaltransducer wheel on the camshaft, for example, no additional sensors,but rather only a simple circuitry, are thus required according to thepresent invention. This makes an engine start possible, even when thephase sensor is defective. The present invention may be usedadvantageously in gasoline direct injection engines in particular, sinceinjection is completely avoided during phase detection and thus no fuelmay reach the catalytic converter. Moreover, the present invention mayalso be used in multipoint injection engines; such a use is particularlyadvantageous in multipoint injection engines in which the conventionallyused twin ignition system, i.e., ignition and injection at each top deadcenter, is problematic.

The measuring device and the analyzing device used according to thepresent invention may be integrated. In particular, no additionalinterference occurs in the primary and secondary circuits during ameasurement of the primary voltage induced at the primary winding, sothat reliable cost-effective phase detection is possible without furtherinterference in the ignition operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail in the followingbased upon the Figures and several example embodiments described below.

FIG. 1 shows a diagram of an ignition system including two alternativelyusable devices for phase detection according to the present invention.

FIGS. 2 a, b show diagrams of the variation over time of the voltagesU_(R1), U2 of FIG. 1 at the top dead centers.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

A primary winding of an ignition coil 2 and an ignition transistor 3 aresituated in a primary circuit 4 between a battery connection of vehiclevoltage UB and ground according to FIG. 1. Ignition transistor 3 istriggered by a control signal a and, in its low-resistance state, i.e.,at high voltage level of control signal a, enables a primary current inprimary circuit 4 via which a magnetic field is created in ignition coil2. During subsequent blocking of ignition transistor 3 in itshigh-resistance state, i.e., at low voltage level of control signal a,the collapsing magnetic field of ignition coil 2 induces a voltage surgein its secondary winding, resulting in a spark discharge at a spark plug8. At this juncture, according to the particular secondary current, avoltage U2 drops across shunt resistor RM, connected in series,vis-à-vis the grounded terminal of ignition coil 8.

According to an example embodiment of the present invention, theignition system shown, including ignition coil 2, vehicle voltage UB,and control signal a, is selected in such a way that, prior to switchingoff the primary current, the ignition power stored in ignition coil 2 issufficient for building up an adequately high ignition voltage at sparkplug 8 for igniting a gas in the charge cycle top dead center (CC-TDC),as well as in the ignition top dead center (I-TDC).

Voltage U1, applied to the collector of ignition transistor 3 or to thecorresponding terminal of the primary winding of ignition coil 2, istapped by a voltage divider circuit having resistors R1, R2. One inputof an operational amplifier 12 or comparator is connected to the voltagedivider circuit between resistors R1 and R2, thus picking up a primaryreference voltage U_(R1)=R1/(R1+R2)U1. Zener diode ZD which is shown maybe connected parallel to R1 for voltage limitation. Resistors R1, R2 areselected in such a way that they do not greatly influence the primarycurrent and that, in particular in the high-resistance state of ignitiontransistor 3, no noteworthy primary current, relevant for the magneticfield of ignition coil 2, flows through them. Due to the fact that,instead of U1, the primary reference voltage U_(R1) is supplied tooperational amplifier 12, a limited voltage value is applied at themoment of ignition, instead of the high voltage value of U1. R2=100 kOhmand R1=11 kOhm may be selected here, so that a current of approximately2 mA flows through R2, and the operating voltage of U1 ranges between 20V and 40 V and the operating voltage of U_(R1) ranges between 2 V and 4V.

The other input of operational amplifier 12 is connected to vehiclevoltage U_(B) via a second voltage divider circuit 13 or via anothersuitable device for setting a reference voltage URef. A referencevoltage URef, dependent on vehicle voltage U_(B), is generated by usingvoltage divider circuit 13, so that an advantageous automatic adaptationto changes in U_(B) takes place (e.g., when the starter is operated). Asa function of U1, operational amplifier 12 delivers a high or a lowoutput signal. URef and R1, R2 are selected here in such a way that aprimary voltage, induced by the secondary current during an ignition,may be detected and differentiated from an ignition current-free state.The output signal of operational amplifier 12 is supplied to a firstanalyzing device 16 which also picks up control signal a and outputs aspark duration signal t-BR1.

The spark duration signals output by first analyzing device 16 andsecond analyzing device 18 may subsequently be compared in a comparator(not shown) with signals of the measurement performed at the subsequenttop dead center.

According to an example embodiment of the present invention, the firstmeasuring device in the primary circuit or the second measuring devicein the secondary circuit may be used alternatively; however, the use ofboth measuring devices and analyzing devices is also possible.

The same control signal a is output during ignition at the top deadcenters offset by 360°, so that the same ignition power is supplied tothe magnetic field of ignition coil 2. According to Paschen's law,however, a different ignition behavior occurs after ignition at I-TDCwhich has high-pressure compressed gas between the electrodes of sparkplug 8 and the CC-TDC which has low-pressure gas between the electrodesof spark plug 8, resulting in varying voltage curves U_(R1) and U2, ascan be seen in FIGS. 2 a, b.

During measuring and analyzing at primary circuit 4 of ignition coil 2,a low voltage value U1 and thus also U_(R1) is initially present in bothpositions of the crankshaft prior to ignition, i.e., in thelow-resistance state of ignition transistor 3. The subsequent ignitionwith an ignition voltage surge SP takes place at the charge cycle TDC ata lower ignition voltage, whereby voltage U1 in the primary circuittakes on a lower value and, according to the LW curve, U_(R1) also takeson a lower value than at ignition TDC according to curve Z. Theparticular spark operation takes place with different spark durationst-BR-I-TDC and t-BR-CC-TDC. The particular measured voltage U_(R1) isproportional to voltage U1 which is induced from the collapsing magneticfield of ignition coil 2. The magnetic field of ignition coil 2 having alarger secondary current in secondary circuit 6 collapses faster atignition TDC, so that a larger voltage U1 having a shorter duration isinduced in the primary circuit. The magnetic field of ignition coil 2collapses more slowly with the formation of a smaller secondary currentin the charge cycle TDC of the LW curve, so that voltage U1 induced inthe primary circuit, and thus also U_(R1), is smaller and has a longerspark duration t-BR-CC-TDC. A reference voltage URef1 is between thevalue of U_(R1) during longer spark duration t-BR-CC-TDC and a staticvalue U_(N) after spark durations t-BR-I-TDC and t-BR-CC-TDC. The sparkduration may thus be determined by comparing U_(R1) with referencevoltage URef1 in operational amplifier 12, the value of the outputsignal of operational amplifier 12 or comparator changing after theparticular spark duration. This output signal of operational amplifier12 is output to analyzing device 16 which picks up control signal a fordetermining the moment of ignition and outputs a spark duration signalt-BR1.

If the second measuring device and second analyzing device are usedalternatively, then according to the curve in FIG. 2 b, a voltage U2,proportional to the induced secondary current, is picked up directlyfrom second analyzing device 18. Measured curves Z of the ignition TDCand the charge cycle TDC shown in FIG. 2 b are not necessarily strictlylinear. The secondary current induced in the secondary winding ofignition coil 2 drops relatively quickly from a high initial value tozero within the spark duration t-BR-I-TDC. The secondary current inducedduring the charge cycle TDC drops from a smaller value to zero over thelonger spark duration t-BR-CC-TDC. These measured curves may bedifferentiated, for example, by comparing voltages U2 shown withreference voltage URef2, depicted using a dashed line, in an operationalamplifier or comparator of analyzing device 18, for example. URef2 is tobe set adequately low in order to obtain a clear difference in themeasured curves.

1. A method for detecting a phase of a four-stroke gasoline engine, comprising: in a starting phase, turning a crankshaft together with at least one piston; triggering an ignition via an ignition coil without supply of fuel at at least two successive top dead centers of the piston; measuring one of: i) a primary current or a primary voltage of a primary circuit, or ii) a secondary current or a secondary voltage of a secondary circuit, in a measuring period which extends at least over a spark duration after the ignition; comparing measurements of successive top dead centers; and determining, based on the comparison, which of the top dead centers is an ignition top dead center between a compression stroke and a power stroke, and which is a charge cycle top dead center between an exhaust stroke and an intake stroke.
 2. The method as recited in claim 1, wherein the measurement identifying a shorter spark duration is assigned to the ignition top dead center.
 3. The method as recited in claim 1, wherein the spark duration is identified as a time period after the ignition in which one of: a primary voltage measured value or a secondary voltage measured value, or ii) a primary current measured value or a secondary current measured value exceeds a reference value.
 4. The method as recited in claim 1, further comprising: within the measuring period, comparing a primary voltage across a primary winding of the ignition coil or a primary reference voltage formed from the primary voltage via a voltage divider circuit with a first reference voltage; and outputting a spark duration signal as a function of the comparison.
 5. The method as recited in claim 4, wherein a first reference voltage is between voltage values of the primary reference voltage during the spark duration of a charge cycle top dead center and a static voltage after the spark duration.
 6. The method as recited in claim 1, wherein the secondary current is determined by measuring a secondary voltage drop across a shunt resistor which is connected in series to a secondary winding and a spark plug.
 7. The method as recited in claim 6, further comprising: comparing the secondary voltages measured at the top dead centers with a second reference voltage; and outputting a spark duration signal as a function of the comparison.
 8. The method as recited in claim 1, further comprising: outputting a spark duration signal as a function of the measurement and a control signal of an ignition transistor.
 9. The method as recited in claim 1, further comprising: determining the phase of a gasoline direct injection engine.
 10. The method as recited in claim 1, further comprising: determining the ignition top dead center in multiple cylinders.
 11. A method for igniting a four-stroke gasoline direct injection engine comprising: determining a phase of the engine and of a crankshaft rotation using a method including the following steps: in a starting phase, turning a crankshaft together with at least one piston, triggering an ignition via an ignition coil without supply of fuel at at least two successive top dead centers of the piston, measuring one of: i) a primary current or a primary voltage of a primary circuit, or ii) a secondary current or a secondary voltage of a secondary circuit, in a measuring period which extends at least over a spark duration after the ignition, comparing measurements of successive top dead centers, and determining, based on the comparison, which of the top dead centers is an ignition top dead center between a compression stroke and a power stroke, and which is a charge cycle top dead center between an exhaust stroke and an intake stroke; and after determining the phase, injecting and igniting according to the phase without interruption of the crankshaft rotation.
 12. A device for detecting a phase of a four-stroke gasoline engine, the engine including a primary circuit, a secondary circuit, an ignition coil, a spark plug, and an ignition transistor, the device comprising: a measuring device configured to measure one of: i) primary voltage or a secondary voltage, or ii) a primary current or a secondary current, during a crankshaft rotation at times of successive top dead centers of a piston without a supply of fuel in a measuring period which extends at least over a spark duration after an ignition, and configured to output a measuring signal; and an analyzing device configured to pick up the measuring signal of the measuring device and output a signal which indicates which of the successive top dead centers is an ignition top dead center between a compression stroke and a power stroke and which is a charge cycle top dead center between an exhaust stroke and an intake stroke.
 13. The device as recited in claim 12, wherein the measuring device is a primary voltage measuring device for measuring a primary voltage induced by the secondary current.
 14. The device as recited in claim 12, wherein the measuring device has a comparator whose inputs are connected to primary winding terminals of the ignition coil via a voltage-setting device.
 15. The device as recited in claim 14, wherein the comparator is an operation amplifier.
 16. The device as recited in claim 14, wherein the voltage setting device includes a reference voltage circuit and a voltage divoder circuit.
 17. The device as recited in claim 14, wherein the analyzing device picks up the measuring signal of the measuring device and a control signal of the ignition transistor and, as a function thereof, outputs a spark duration signal to the comparator.
 18. The device as recited in claim 17, wherein the comparator has a memory element for intermediate storage of at least one spark duration signal of one measurement for comparison with the spark duration signal of a subsequent measurement.
 19. The device as recited in claim 12, wherein the measuring device is a secondary current measuring device which has a resistor which, in a secondary circuit, is connected in series with a secondary winding of the ignition coil and the spark plug, the analyzing device picking up a secondary voltage drop across the resistor, as the measuring signal. 